A conventional teaching operation is shown in FIG. 1. As shown, a teaching operation of a six-axis articulated robot, one of the following motion controls is carried out when the orientation of a workpiece 4 clamped is a tool (not shown) at each wrist flange of the robot as shown in FIG. 1(a) is changed to a desired relative orientation as shown in FIG. 1(c) with respect to an arbitrary working point A of a teaching operation tool 3:
(1) Each axis of the robot is controlled independently of the others, whereby a desired workpiece orientation is determined.
(2) A desired workpiece orientation is determined by the rotation around a reference coordinate axis on the main body of a robot and parallel displacement to the reference coordinate axis. (FIG. 1(b) and 1(c)).
(3) A desired workpiece orientation is determined by the rotation around the tool coordinate axis on the main body of the robot and parallel displacement to the tool coordinate axis. (FIGS. 1(b) and 1(c)).
The rotations described in (2) and (3) accomplish motion control by rotating around a control point R of a robot.
In method (2), the reference coordinate axes are defined by the reference coordinate axes (X.sub.R, Y.sub.R and Z.sub.R) which, in turn, define the coordinate system of the robot. In method (3), the tool coordinate axes refer to coordinates of a tool attached to the wrist flange of the robot.
However, according to the above-described methods, the workpiece 4 clamped by the robot assumes the desired orientation with respect to an arbitrary working point A by a method involving the control of each axis of the robot independently and the rotation of the workpiece around a coordinate axis with the control point R of the robot as the center of rotation with this method. The orientation of the workpiece 4 along cannot be changed without changing the position of the point P on the workpiece 4, meaning that the rotation and the parallel displacement must be repeatedly carried out, as shown in FIG. 1, resulting in a longer reaching operation time.